Guitar amplifier



FIG. 1 is a front perspective view showing my new design for a guitar amplifier;

FIG. 2 is a left side view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a front view thereof;

FIG. 5 is a rear view thereof;

FIG. 6 is a top view thereof, and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a guitar amplifier, as shown and described. 